1. Field of Invention
The present invention relates to an optical input device, and more particularly to a pen-like optical input device.
2. Related Art
With the rapid development of science and technology, computer operating systems are widely used in daily life. Generally speaking, when operating a computer operating system, a user must control the movement of a cursor through peripheral input devices such as a mouse, a touchpad or a trackball, so as to input operating instructions on a window interface of the computer. Taking an optical mouse as an example, in addition to functions of the common optical mouse such as moving the cursor and clicking/selecting page data, currently in the structure design of the optical mouse, the input devices such as an optical pen or a pen-like optical mouse have been developed so that the user can use the optical mouse to write or underline and comment the page data.
For example, U.S. Pat. No. 6,151,015 has disclosed a pen like computer pointing device, in which a light emitting diode (LED) or a laser LED, an optical sensor and a lens are disposed in a pen like case. A light ray generated by the LED is projected to a work surface, for example, a desk. After a reflected light ray of the light ray is generated on the work surface, the reflected light ray is refracted to the optical sensor through the lens, such that the optical sensor detects a change of the light ray and forms an image, thereby generating a corresponding cursor movement signal and inputting the signal to the computer. When the pen-like optical mouse moves, a movement track thereof is recorded as a group of continuous images shot at a high speed. Finally, the shot images are analyzed and processed by an interface microprocessor inside the optical mouse, and changes of positions of feature points on these images are analyzed, so as to determine a moving direction and moving distance of the mouse and complete the location of the cursor.
However, currently in this type of optical mouse, the lens and the optical sensor are disposed in the case in parallel, that is, a direction of an optical axis of the lens is parallel to that of the normal of the optical sensor. Therefore, when the user operates the pen-like optical mouse in a general pose like holding a pen (for example, the penholder inclines to the work surface), since the optical axis of the lens inclines to the work surface, an object distance of the lens relative to the work surface is changed (extended or shortened).
However, in the case that a focal length of the lens and a sensing range of the optical sensor are fixed, when the object distance between the lens and the work surface changes, an imaging range formed after the reflected light ray is refracted by the lens fails to fall into the focus. For instance, the imaging range of the reflected light ray exceeds the sensing range of the optical sensor, which results in the generation of a blur image since the reflected light ray cannot be completely imaged on the optical sensor, causing confusion when the optical sensor reads an optical signal and degrading the quality (for example contrast) of the image detected by the optical sensor, and even resulting in errors in locating the cursor.